The steering angle or steering angle lock values in motor vehicles influences a driving dynamics control system. In addition to the steering angle values, a driving dynamics control system obtains further measurement data such as the wheel rotational speed or the rotation of the motor vehicle about its vertical axis. The absolute steering angle lock and the steering rate are required so that these values can be evaluated together with the other detected data by the driving dynamics control system. All the data can then be converted for controlling actuators such as brakes and for managing the engine.
An optoelectronic steering angle sensor is disclosed, for example, in DE 40 22 837 A1. The disclosed steering angle sensor includes a light source and a line sensor arranged in parallel and spaced apart from each other and an encoder disc (code transmitter) disposed between the light source and the line sensor. The encoder disc is non-rotatable connected to the steering spindle. The line sensor is a CCD-sensor line. The code transmitter is a light slit disc and includes as a code trace a spiral which increases in size from the inside outwards. From the exposure of the image points of the line sensor in the case of a specific steering lock it is possible to obtain information regarding the actual steering angle lock.
In order that the steering angle data obtained can be used for further processing as an input variable of a driving dynamics control system the data must be highly accurate and have the highest possible resolution. These desired requirements cannot be met by the steering angle sensor or the method which are disclosed in DE 40 22 837 A1. Because the encoder disc is non-rotatable disposed on the steering spindle and the line sensor is fixed in position with respect to the rotational movement of the encoder disc and is thus not attached to the steering spindle, any movements of the steering spindle causing it to move in directions perpendicular to the longitudinal axis are detected as a change in the steering angle lock by the corresponding movement of the encoder disc and the associated movement of the code trace imaged on the line sensor. Accordingly, the driving dynamics control system is also influenced with this type of incorrect information.
The measurement accuracy of the previously known steering angle sensor is determined by the accuracy and the fineness of the code trace and by the imaging sharpness of the light trace of the encoder disc on the line sensor. In order to achieve the most effective imaging sharpness the previously known steering angle sensor uses an elongated light source such as a line-source LED or a longitudinal light source. The length of these light sources corresponds to the length of the sensor line. The emitted light beams impinge upon the surface of the code transmitter at right angles where possible. This feature is intended to achieve the most discrete bright-dark light transition possible in order to be able to exactly determine the light trace on the line sensor. These demands require the encoder disc to be assembled and adjusted precisely with respect to the light source and the line sensor. The resolution which can be achieved even when using a highly accurate code trace corresponds to the physical resolution of the line sensor. Consequently, the resolution of this type of steering angle sensor can be increased merely by using a line sensor with an extremely high number of image points and a code trace having an extremely precise line. However, these features require considerable outlay and place high demands upon the tolerances which are to be maintained.